Gr-s cured with dicamyl peroxide and sulfur



United -tates Patent GR-S cunnn WITH DICAMYL PEROXIDE AND SULFUR William D. Willis, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware N Drawing. Filed Dec. 4, 1956, Ser. No. 626,076

4 Claims. (Cl. 260-795) where R and R are aryl groups and R R R and R are hydrogen or alkyl groups of less than 4 carbon atoms, are extremely elfective vulcanizing agents for both natural and synthetic rubber. In fact, through the use of this class of peroxides as a vulcanizing agent for all types of rubber, it is possible to produce vulcanizates which are superior in many respects to vulcanized rubbers prepared using any other vulcanizing agent known to the art.

In accordance with the present invention, it has been found that in the vulcanization of synthetic rubber prepared by the copolymerization of a major amount of butadiene and a minor amount of styrene (generally known as GRHS) there is advantage to begained by employing as the vulcanizing agent a combination of sulfur and a peroxide of the formula given above. The invention is thus directed to the vulcanizable rubber composition comprising a synthetic rubbery copolymer of butadiene and'styrene and minor amounts, eifective to promote vulcanization at an elevated temperature, of sulfur and a di(aralkyl) peroxide having the structural formula:

where. R and R are aryl groups and R R R and R are selected from the class consisting of hydrogen and alkyl groups of less than 4 carbon atoms. A particularly preferred species of peroxide is bis(a,a-dimethyl benzyl) peroxide.

Through the practice of the invention, it is possible to prepare vulcanizates of improved physical properties, in particular, vulcanizates having improved tensile strength and modulus. This will be illustrated by the following example in which parts and percentages are by weight.

EXAMPLE Using a conventional two roll rubber mill, at rubbery butadiene-styrene copolymer (GRS X732) was blended with disproportionated rosin in the ratio of 80 parts of the former to 20 parts of the latter. This rosin-extended synthetic rubber was then blended with additional ingredients in preparing two homogeneous compositions ofthe following formulation:

Table I Rosin-extended GR-S X732 -l 100 Furnace black Zinc oxide Stea-ric acid N-eyclohexyl-Z-benzothiazole sulfenamide ggfg'amethyl thiuram disulfide ur Bis(a,a-dimethylbenzyl) peroxide S il r-2 P root- 00088 Table II Cure Time (Minutes) Modulus at 300% Elongation (p.s.i.)

Shore A Hardness 0365 me. NNSQM Bashore Resilience From the preceding data, the improvement in modulus and tensile strength is evident, particularly at cure times of less than minutes.

The peroxides of this invention are di(aralkyl) peroxides having the structural formula:

where R is an aryl group, R R R and R are hydrogen or alkyl groups of less than 4 carbon atoms, and R is an aryl group. R R R and R may all be the same or each may be a different group or any two ormore may be the same or different. Similarly, R and R may be the same, or difierent, aryl, groups.

The aryl groups referred to in the above formula may,

. 3. for example, be phenyl, naphthyl, anthryl, phenanthryl, and the like. The aryl groups may contain alkyl substituents as in the case of methylphenyl, ethylphenyl, propylphenyl, isopropylphenyl, butylphenyl, isobutylphenyl, t-butylphenyl, pentamethylethylphenyl, dimethylphenyl, methylethylphenyl, etc., and corresponding alkyl derivatives of the other aryl groups mentioned. The

term aryl as used herein includes alkaryl groups. When an alkyl substituent in an aryl group contains less than 4 carbon atoms, it may be the same as or difierent from any of R R R or R Aryl groups in which the alkyl substituents, if any, contain less than 8 carbon atoms are preferred.

The class of di(aralkyl) peroxides of this invention include the following symmetrical or bis(aralkyl) peroxides: dibenzyl peroxide, bis(u-methylbenzyl-) peroxide, bis(u-ethylbenzyl) peroxide, bis(a-propylbenzyl) peroxide, 'bis(a-isopropylbenzyl) peroxide, bis(a,a-dirnethylbenzyl) peroxide, bis(u-methyl-a-ethylbenzyl) peroxide, bis(a,u-diethylbenzyl) peroxide, bis(a,a-diprop lbenzyl) peroxide, bis(u,a-diisopropylbenzyl) peroxide, bis(a,a-

diisopropylnaphthylmethyl) peroxide, bis(a,a-dimethylnaphthylmethyl peroxide, bis a, a-dimethyl-p-methylben- -zyl) peroxide, bis(a-methyl-a-ethyl-p-methylbenzyl) peroxide, bis(a,a-diethyl p-methylbenzyl) peroxide, biS(u,ct-

diisopropyl-p-methylbenzyl) peroxide, bis(a,a-dimethyl-pethylbenzyl) peroxide, bis(u-methyLu-ethylp-ethylbenzyl) peroxide, bis(a, x-diethyl-p-ethylbenzyl) peroxide, bis'(a,ot-diisopropyl-p-ethylbenzyl) peroxide, biS(oc,oc-dimethyl-p-isopropylbenzyl) peroxide, bis(a-methyl-u-ethyl- ,p-isopropylbenzyl) peroxide, bis(a,a-diethyl-p-isopropylbenzyl) peroxide, bis(a,a-diisopropyl-p isopropylbenzyl) peroxide, bis(a,ot-dimethyl-p-t-butylbenzyl) peroxide, his- (a methyl a ethyl p t butylbenzyl) peroxide, bis(u,a-diethyl-p-t-butylbenzyl) peroxide, bis(a,a-diiso'- propyl-p-t-butylbenzyl) peroxide, bis(a,a-dimethyl-p-pentamethylethylbenzyl) peroxide,

benzyl) peroxide, benzyl OL-IIlGthYl-P-iSOPI'OPYibCIIZYl) peroxide, benzyl(a,a-dimethylbenzyl) peroxide, benzyl- (a,u-dimethyl-p-methylbenzyl) peroxide, benzyl(a,u-dibis(a-methyl-a-ethyl-p' pentamethylethylbenzyl) peroxide, bis(a,ot-diethyl-p-penmethyl-p-isopropylbenzyl) peroxide, a-methylbenzyl(a,a-

dimethy-lbenzyl) peroxide, a-methylbenzyl(m,m dimethylp-methylbenzyl) peroxide, a-methylbenzyl(a,a-dimethylp-isopropylbenzyl) peroxide, a-isopropylben'zyl(,a diiso .propylbenzyl) peroxide, a,a-dimethylbenzyKa,a-dimethylp-methylbenzyl) peroxide, a,a-diisopropylbenzyl(a,a-diisopropyl-p-methylbenzyl) peroxide, and a,u-diisopropyl- .'benzyl(a,u-diisopropyl-p-isopropylbenzyl) peroxide.

' In general the peroxides of this invention are characterized by containing at least 14 carbon atoms and usually not more than about 40 carbon atoms.

peroxides containing 14 to about 25 carbon atoms are preferred as producing'very desirable vulcanizates and because they may be prepared from readily available materials. The symmetrical peroxides of this invention are exceptionally useful. since in addition to producing vulcanizates havingextraordinary properties they can be prepared in higher yields more easily than the unsymmetrical peroxides. Specific peroxides preferred in this invention are bis(oi,u-dimethylbenzyl) peroxide, bi$(a,0c-

dimethyl-p-methylbenzyl) peroxide, and bis(u,u-dimethylp-isopropylbenzyl) peroxide;

In addition to the peroxide, the invention also requires the presence of sulfur as a vulcanizing agent in order to obtaintheadvantages of the invention. The respective quantities of sulfur and ofperoxide are, however, widely variable and .optimum quantities 'of each vulcanizing agent will vary accordingto the nature of the composi tion, i.e., whether an accelerator is present or not, what type of filler is employed, etc. Generally, however, the amount of peroxide will vary from about 0.01 to about 10% by weight of the rubber and the amount of sulfur will vary from about 0.05 to about 3% by weight of the rubber.

When utilizing the invention, it is apparent that suitable fillers, reinforcing agents, antioxidants, extenders, plasticizers, softeners, processing aids, and other ingredients commonly used in the vulcanization of butadiene-styrene rubber can be employed.

Zinc oxide, reinforcing grades of carbon black, and the like, may be employed as reinforcing agents. Preferably, a mixture of suitable fillers and reinforcing agents is employed to give to the compositions the particular properties which may be desired. Thus, a mixture of zinc oxide and carbon black may be employed in the manner illustrated by the examples. Suitable pigments, such as ultramarine, vermillion, or the like, maybe employed to impart to the composition a desired color. Asa means for obtaining vulcanization of the composition at lower temperatures or for increasing the rate of vulcanization suitable accelerators may be employed. Accelerators which are familiar to the art are, in general, satisfactory. The effects of various accelerators upon the vulcanization of the composition and upon its properties after vulcanization vary somewhat and thereby provide vulcanized product.

like hereinbefore mentioned is well known, and one skilled in the art will have no difliculty in arriving at a formulation suitable for a particular need. 7

Preparation of the vulcanizable composition and the vulcanization procedure follow the practices of the art. The compositions are prepared, for example, by the simple practice of milling the ingredients together on any of the common types of milling apparatus. Vulcanization is effected by heating to a temperature ranging from 'about 270-375" F. and optimum temperatures within this range will vary according to the nature of the compounding ingredients. What I'claim and desire to protect by Letters Patent is: 1. A' vulcanizable rubber compositionrcomprising a synthetic rubbery copolymer of butadiene and styrene, sulfur in an amount from about 0.05 to about 3% by weight of the rubbery copolymer and bis(a,a-dimethylbenzyl) peroxide in an amount from about 0.01 to about 10% by weight of the rubbery copolymer.

2. The composition of claim 1 wherein there also is present a vulcanization accelerator selected from the group consisting of N-cyclohexyl-Z-benzothiazole sulfenamide, tetramethyl'thiurarn disulfide and mixtures thereof. a

'3. The process for preparing a vulcanized rubber which.

References Cited in the'file of this patent UNITED STATES PATENTS 1,249,181

Ostromislensky Dec. 4, 19%17 2,426,476 Vaughan et al Aug. 26, 1947 2,668,180 Boardman Feb. 2,1954 2,691,683 Lorand et a1. Oct 12, 1954 2,717,914 Harbison Sept. 13, 1955 2,819,256 Boardman 'Jan. 7, 1958 The use of the various fillers, antioxidants, and the 

1. A VULCANIZABLE RUBBER COMPOSITION COMPRISING A SYNTHETIC RUBBERY COPOLYMER OF BUTADIENE AND STYRENE, SULFUR IN AN AMOUNT FROM ABOUT 0.05 TO ABOUT 3% BY WEIGHT OF THE RUBBER COPOLYMER AND BIS-(A,A-DIMETHYLBENZYL) PEROXIDE IN AN AMOUNT FROM ABOUT 0.01 TO ABOUT 10% BY WEIGHT OF THE RUBBERY COPOLYMER. 